1. Field of the Invention
The present invention relates to a method for lapping a material to be lapped such as a semiconductor wafer and also relates to a method for manufacturing lapping particles for use in the lapping method.
2. Description of the Related Art
FIG. 1 shows an example of method for lapping the semiconductor wafer, in which the semiconductor wafer, the material to be lapped, is pressed to contact with a lapping cloth held on a holding table. The lapping cloth is supported on a rotating table not depicted in the figure. Lapping may be performed by rotating the lapping cloth along with supplying a lapping agent onto a lapping cloth surface contacting with the wafer.
The lapping agent is obtained by mixing lapping particles of silica or alumina into a liquid medium and adjusting a particle diameter and pH thereof. In the conventional lapping method, a counter plan for scratches and dishing is essentially achieved by adjusting the hardness of the lapping cloth.
Japanese patent application laid-open No. 04-223852 describes a lapping method based on such the concept. In this known method, the lapping is performed with using a grindstone of a low bonding property type, which contains grindstone particles with a slightly higher hardness than that of the material to be lapped. The method also employs simultaneously other lapping particles with a hardness equivalent to or slightly lower than that of the material to be lapped. A metal oxide such as a chromium oxide, iron oxide, silicon oxide and magnesium oxide and a magnesium carbonate are recommended for use in the lapping particles.
Japanese patent application laid-open No. 08-3540 discloses an example of method for manufacturing lapping particles for use in such the lapping. In this conventional method, the hardness of the lapping particles may be adjusted by emulsion-polymerizing an organic metal compound having a metal-oxygen interatomic bond to form micronized particles of a metal oxide series compound with a relatively lower hardness, and thereafter generating another metal oxide series compound with a relatively higher hardness around the micronized particles.
In case of the material such as an Al-CMP for forming an Al damascene, however, the dishing and scratches may be caused easily because of softness of Al.
In addition, an optimum kind of lapping particles is intentionally adapted to the material, which is selected from various lapping particles by essentially changing the kind thereof. As the hardness of the lapping particles is not adjusted particularly, however, adjusting only the hardness of the lapping cloth can not remove the scratches caused from the lapping particles. This is mainly due to that the hardness of the lapping particles is not adjusted as well as that of the lapping cloth together.
Such the method for manufacturing lapping particles as described in the above-mentioned Japanese patent application laid-open No. 08-3540 may provide lapping particles having a relatively high hardness. However, an adjustable range thereof is limited. With respect to the hardness control, described are the selection of the structure and the like of the organic metal compound to be used as the raw material, and the calcination after the generation thereof. These are directed to increase the hardness of the lapping particles.
An object of the present invention is to provide a lapping method capable of preventing the generation of dishing and scratches.
Another object of the present invention is to provide a method for manufacturing lapping particles suitable for the above lapping method.